The following invention relates to a system for ranging and speed detection, and more particularly relates to an optical system for determining range and speed that is passive and does not require an energy transmitter to accomplish its purpose.
Most speed detection systems require a transmitter to transmit energy towards a moving target which is reflected back to a receiver. Various schemes are then provided for measuring the time of transmission and the return of the energy in order to calculate the range to the target and its speed. Radar is a primary example of this technique, and radar guns are conventionally used by law enforcement agencies for traffic control. The problem with radar as a traffic control device is that target acquisition and measurement are ambiguous. It can frequently not be determined which target out of a multitude of possible targets is responsible for generating any particular speed indication. Another problem is that radar can be detected by receivers tuned to the proper frequency. Laser ranging systems are also available but such systems are also detectable at the target and are prohibitively expensive.
In the past there have been attempts to design purely optical speed measuring systems, but all suffer from one or more defects regarding accuracy or cost of implementation. For example, passive optical systems are available which calculate an oncoming object's velocity by acquiring images at two different times and comparing the relative sizes of the images in the field of view as a function of time. Examples of such devices are shown in the U.S. patents to Goodrich U.S. Pat. No. 4,257,703, Abel U.S. Pat. No. 3,788,201 and Michalopoulous et al. U.S. Pat. No. 4,847,772.
Other prior art devices utilize trigonometric relationships by capturing an image at different times at known marker positions. Such systems are shown in Tyssen et al. U.S. Pat. No. 4,727,258 and Young et al. U.S. Pat. No. 4,135,817. These systems, however, require that the time of capture of an image be synchronized with the appearance of the target object at a known marker position. This is not always practical and sometimes requires that the cameras be spaced widely apart or placed at different locations.
These and other prior art passive optical speed detection systems are generally overly complex and/or impractical or require external markers and the like. What is needed, therefore, is a practical, compact, low cost, optical speed and/or distance detecting system which can be used at any desired location with a minimum of set-up time and complexity.